1. Field of Invention
The present invention relates to a fiber optic transceiver module to optically couple a light emitting element or a light receiving element and an optical fiber and electronic equipment.
2. Description of Related Art
Optical fibers are used in optical communications systems to transmit laser beams and establishing communications. At the end of each optical fiber, a module for optical communications that includes a light emitting element or a light receiving element is installed. In installing this module, for example, the light emitting element, a lens, and the end of a core of the optical fiber are precisely aligned in three dimensions so as to efficiently lead light emitted from the light emitting element to the core of the optical fiber. See Japanese laid-open patent application No. 5-243688, for example.
The above-mentioned related art module for optical communications requires precise alignment among a light emitting or receiving element, a lens, and the end of a core of an optical fiber, to avoid a condition that each of these elements is out of alignment in three dimensions, thus consuming time and cost to install the module. Specifically, in order to install the module, a light emitting element, a lens, and an optical fiber are roughly aligned first. Then, light is emitted from the light emitting element. Subsequently, the alignment among the light emitting element, the lens, and the end of the optical fiber is finely adjusted in three dimensions so as to have light focused on the lens and directed into the end of the optical fiber.
A back reflection (returned light) at an end of the optical fiber may cause problems in a module for optical communications. The returned light problem will now be described by referring to FIG. 29. A fiber optic transceiver module 200 shown in FIG. 29 includes a block 211 including a optical waveguide 212 and a guide 13 and a light emitting element 201 attached on a side 214 of the block 211. An optical fiber 60 including a core 62 and a clad 61 is inserted into the guide 13. This makes it possible to transmit light emitted by the light emitting element 201 through the optical waveguide 212 to enter the core 62 of the optical fiber 60.
A part of the light emitted by the light emitting element 201 is reflected as a returned light R1 at the end of the optical waveguide 212 and a returned light R2 at the end of the core 62. For example, the light emitting element 201 may be a semiconductor laser (an edge emitting laser or an surface emitting laser). The returned light R1 and R2 enter the semiconductor laser so as to cause an unstable laser oscillation. A reflection mirror at an end of the laser plays a role of a resonator. Hence, if the emitted light returns, this returned light functions as a plurality of resonators so as to fluctuate an oscillation frequency. When using a laser as a light source in optical signal communications, it is always required to minimize the amount of the returned light for stable laser oscillation.
As for a countermeasure for the returned light, a method of filling transparent resin (called potting resin or matching resin), whose refractive index is similar to that of the optical fiber (core), is adopted. However, the method is not able to avoid the returned light effectively in normal surrounding conditions where temperatures vary, because of a temperature dependency of a refractive index of the potting resin. When the potting resin is applied to couple the guide to the optical fiber, a method allowing the block and the optical fiber to couple or decouple conveniently is not applicable. Specifically, the application is limited.
Alternatively, a method to cut the end of the optical fiber at an angle was introduced. The method, however, is also not able to cope with the returned light reflected from a part excluding the end of the optical fiber (for example, the end of the optical waveguide) and further the processing of the end of the optical fiber is expensive.